So the heater is just about ten years old then. First check out your lower element with the power off and the wires disconnected, you should get a resistance reading across the heating coil, with an ohm meter, if you dont the element is burnt and needs to be replaced. If you have resistance across the element hook it back up and turn on the power. Now check to see that both the lower and higher thermostats are working, or which one isnt. Or you may want to check the price of a upper and lower t-stat, add them together along with an element and your time and decide that it cheaper to replace the whole tank. I have heard of electric tanks being as low as 125 dollars, and the upper control can sometimes set you back half of that…….LOu